2 WHAT AKE ANIMALS? 



the outset -what animals are ; or, in other words, to know 

 what constitutes an animal. 



While all intelligent persons recognize as animals, Man, 

 monkeys, the beasts of the forest, the cattle and sheep of 

 the meadows, the birds of the air, the fishes of the waters, 

 and all other similar forms, it must here be understood 

 that it is not easy and perhaps not possible in the present 

 condition of science to state in precise terms exactly what 

 animals are; or, in other words, to frame a definition 

 which shall apply to all animals, to the lowest as well as 

 to the highest forms, and which shall not apply to any of 

 the forms of plants. 



So far as regards the higher forms of animals and plants, 

 there is little or no difficulty in defining them ; but the 

 difficulty arises when the naturalist has to deal with the 

 lower, and especially with the microscopic forms of life.* 



*In view of the great difficulty in drawing an exact line of separation be- 

 tween Animals and Plants, Haeckel has recommended the recognition of an 

 intermediate Kingdom to be called the Regntim Protisticum, in which all 

 organisms shall be included which cannot with certainty be referred either 

 to the Animal Kingdom on the one hand, or the Vegetable Kingdom on the 

 other. Kcgnum Protisticum literally means the kingdom of simplest or- 

 ganisms. 



As it is not yet proved that there is really any such intermediate Kingdom 

 in nature as is here suggested, the recommendation of Haeckel cannot at 

 present be adopted. 



"Irritability, contractility, locomotion, and the 'cyclosis,' or circulation 

 of absorbed and assimilated nutritive matters, are phenomena universal in the 

 animal, and occasionally -observable in the vegetable kingdom ; whilst the 

 secretion of chlorophyll, and of cellulose, and the power of regenerating an 

 entire compound organism from a more or less fragmentary portion, are 

 properties nearly, though not quite universal in vegetables, and only occasion- 

 ally noticeable among animals. It may be anticipated, that in the few cases 

 in which it may at present be difficult to decide with perfect certainty as to 

 the animal or vegetable character of an organism, an increase in our knowl- 

 edge, if not of its very simple structure, yet of its development, and if not of 

 cither its development or its structure, yet of the development and structure 

 of forms which by gradual transitions connect it with undoubted animal or 

 undoubted vegetable forms, is likely at some time to enable us to place it 



